Objective To evaluate the effects of inhaled bronchodilators on respiratory mechanics in moderate and severe chronic obstructive pulmonary disease（COPD） patients during eupnea.Methods Twenty moderate to severe COPD subjects were divided into three groups.Lung function，Borg score，breathing pattern and respiratory mechanics indexes were measured at baseline and 30 min after inhaled placebo，salbutamol 400 μg (or ipratropium 80 μg)，and ipratropium 80 μg (or salbutamol 400 μg) in sequence at interval as specified in different groups.Results In all groups，inhaled bronchodilators improved lung function (FEV1，FVC，IC) (Plt;0.05)，decreased Pdi，Peso，PTPdi，PTPeso and Raw (Plt;0.05，respectively)，in comparison with placebo.The reduction of PTPeso was positively correlated with the reduction of Peso (r=0.713，Plt;0.01）and Raw (r=0.602，Plt;0.01).Borg score decreased after inhaled bronchodilators (Plt;0.05).The reduction of dyspnea was positively correlated with the reduction of inspiratory work of breathing (ΔPTPeso%) (r=0.339，Plt;0.05) and Raw (ΔRaw) (r=0.358，Plt;0.05)，while was not associated with the changes of FEV1，FVC and IC.Conclusions In COPD patients，inhaled bronchodilators can reduce inspiratory work of breathing and airway resistance，the reduction of inspiratory work of breathing contributed to the reduction of airway resistance.Alleviation of dyspnea by inhaled bronchodilators is suggested to be ascribed to reduction of airway resistance and inspiratory work of breathing.
Objective To investigate the changes of respiratory mechanics in response to elevated respiratory central drive and their impacts on the inspiratory signals detection.Methods 10 normal volunteers were recruited for the study from the colleagues of the State Key Laboratory of Respiratory Disease. Rebreathing method was used to increase the end expiratory PCO2 ( PCO2 -ET) to the subject’s maximal tolerance in order to stimulate the increase of respiratory central drive. The changes of respiratory mechanics in response to elevated respiratory central drive and their impacts on the initiation signals of inspiration were observed.Results After re-breathing, the average maximal tolerated PCO2 -ET was ( 81. 2 ±6. 6) mm Hg. As the PCO2 -ET rising, electromyogram of diaphragmatic muscle ( RMSdi ) ,transdiaphragmatic pressure ( Pdi ) and tidal volume ( VT ) increased progressively while the time of respiratory cycle ( Ttot ) shorten gradually. As the PCO2 -ETlevel increased frombaseline [ PCO2 -ET( level-0) ] to the maximal level [ PCO2 -ET( level-4) ] , RMSdi increased from( 17. 17 ±12. 41) μV to ( 147. 99 ±161. 64) μV,Pdi and VT increased from ( 7. 5 ±1. 7) cmH2O and ( 0. 68 ±0. 27) L to ( 26. 13 ±11. 51) cm H2O and ( 2. 21 ±0. 37) L respectively, while Ttot shorten from ( 2. 91 ±0. 85) s to ( 1. 92 ±0. 39) s. These four parameters of respiratory mechanics, RMSdi, Pdi, VT and Ttot, were highly correlated linearly with PCO2 -ET ( r value was 0. 956, 0. 973,0. 956 and 0. 89 respectively, all P lt;0. 001) . At the start of inspiration, the first detectable signal was electromyogramof diaphragmatic muscle ( RMSdi) , followed by mouth pressure ( Pm)and inspiratory flow ( Flow) on time sequence. As the rising of PCO2 -ET, the time lag of Pmand Flow from RMSdi after the initiation of inspiration increased gradually. However, the time lag between Flow and Pm remained constant. Conclusions At the start of inspiration, the signal of RMSdi appears first as compared with Pm and Flow. As the rising of PCO2 -ET, the time lag of Pmand Flow fromRMSdi after the initiation of inspiration increased gradually, suggesting RMSdi is more sensitive inspiratory signal, which might be used for triggering of ventilator in order to improve the synchronization, especially in the situation of elevated respiratory central drive.